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Question

I am working on an app that uses MongoDB (I use Mongoose) as its database.

I have a question, suppose I have this kind of schema:

 [{ "user_id":"2328292073" "username":"Bob", "subscriptions":[ { "id":"38271281, "payments":[ { "id":"00001", "amount":"1900" }, { "id":"00002", "amount":"2000" }, { "id":"00003", "amount":"3000" } ] } ] }]

In my case I want to get the payments array for subscription with id = '38271281' of user with id '2328292073', but I just want to retrieve the payment array, nothing else

My query is the following:

 Mongoose.findOne({ "user_id": "2328292073", "subscriptions.id": "38271281" }, { "subscriptions.payments": 1 })

But I get the entire document of subscriptions. How can i get the payment array only?

Answer 1

you can try using unwind if you want filteration from db only.

Mongoose.aggregate([
  {
    '$match': {
      'user_id': '2328292093'
    }
  }, {
    '$unwind': {
      'path': '$subscriptions'
    }
  }, {
    '$match': {
      'subscriptions.id': '38271281'
    }
  }
])

if you will have multiple documents having same subscription id then you have to group it.

• using code level filter function can also be one another approach to do this.

Answer 2

You can try aggregation operators in projection in find method or also use aggregation method,

• $reduce to iterate loop of subscriptions and check the condition if id matched then return payment array

db.collection.find({
  "user_id": "2328292073",
  "subscriptions.id": "38271281"
},
{
  payments: {
    $reduce: {
      input: "$subscriptions",
      initialValue: [],
      in: {
        $cond: [
          { $eq: ["$$this.id", "38271281"] },
          "$$this.payments",
          "$$value"
        ]
      }
    }
  }
})

Playground